The fanciful design of the Smithsonian Castle150 years old in Decemberbucked the neo-classical trend of Washington's other monuments and buildings.

The cornerstone of the Smithsonian Castle was laid in 1847. It's the oldest of the monumental buildings on the National Mall, and familiarity hasn't dimmed its original visual power. In the 1840s, the heritage of earlier great buildings in the capital (the Treasury Building, Patent Office, Post Office) was neo-Classical, linking the nation's democratic character to democracy's ancient beginnings. But James Renwick, the architect who won the Smithsonian commission when he was not yet 30 years old (and who subsequently designed St. Patrick's Cathedral in New York City) used a medieval revival style—turrets and towers in place of colonnades—to link the Institution instead to a tradition of learning and universities. The Smithsonian was to have the mind's own boundless independence.

At the start, the Castle held the entire Smithsonian. More than a century and a half later, it still identifies the Institution to the world. That's only fitting, because the various identities assumed by one or another area of Renwick's building blossomed over the years into the profusion of individual Smithsonian museums. Recall that in the earliest debates about what the Smithsonian should be, the alternatives included a scientific research institute, an astronomical observatory, a library, a museum, an art gallery and even a teachers college. The ruddy sandstone exterior of the Castle looks today much as it did in 1854, when the building was officially completed. But the interior has known hardly a moment's peace in 150 years. As the Smithsonian grew and its mission evolved, the space underwent continual reconfiguration. Walls, floors, ceilings and balconies, not to mention carpets, colors and furnishings, came and went and came again. (The changes are vividly portrayed in The Castle: An Illustrated History of the Smithsonian Building by Cynthia R. Field, Richard E. Stamm and Heather P. Ewing, published by Smithsonian Books.)

In fact, the building was altered even before it existed: Renwick conceived the central portion with three stories, but one of those floors was lost to preconstruction cost cutting. The great hall on the first floor (now a visitors' center) was originally intended to be a library and a lecture hall. By the time the building opened, it had become a space for displaying natural history specimens; many years later, parts of it would take a turn as a library and a site for graphic arts exhibits. A great hall directly above the lower hall was first meant to be exhibition space. When the building opened, it held instead a lecture hall seating 1,500 to 2,000 people, a scientific apparatus room and an art gallery. But that configuration did not survive a disastrous fire in 1865. When the second floor was rebuilt, it belatedly became, and for more than 40 years remained, exhibition space. The upper hall was eventually compromised into two levels of offices. If you stand on the Mall and face the building, you can see that in the central portion to the left and right of the entrance, Renwick designed the upper windows to light a single story of generous height. Still grand on the exterior, the windows have been divided within by the insertion of a new floor.

The approaching 150th anniversary of the Castle's completion—in December—is, in a sense, nothing of the sort because the building has never really been completed. It's been in a state of perpetual becoming, like the Smithsonian itself. The historic interior and exterior need tending once again, to modernize utility systems and shore up walls and roofs. But the building will stay anchored to its 19th-century origins, and to traditions older still. In photographs from the 1850s, the fanciful new Castle sprawls in isolation on its stretch of barren national ground. Before the surrounding trees grew tall, an observer could take its measure from almost any angle, and from as far away as downtown Washington. In time, the Castle would share the location with other museums, but seen from the right perspective, even in their company, it still stands alone.

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